One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that is flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (“ABS”) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
During the manufacturing process of a mass storage device, all defective sectors found during media test are identified as bad to avoid any further usage. These defects are known as manufacturer's defects and are compiled into a defect list, which is then stored in a reserved area on the disk.
When a storage device is operational out in the field, additional sectors on the media may become defective. These defective sectors are known as “grown” defects.
Currently, the disk controller/firmware uses two types of a defect management method to avoid and compensate for these defective sectors. The first method is known as “defect slipping”and is used to compensate for the manufacturing defects. The second method is known as “defect reassignment” and is used to compensate for grown defects. Using the defect slipping process, defects found during the manufacturing process are slipped. That is, the defective sectors are simply skipped, and sector numbering is continued at the next available good sector. The unused sectors located at the end of the disk are used to replace the lost sectors. This is one method as all the data sectors can be accessed in a contiguous sequence in one revolution.
In the defect reassignment process, when a new defect is found in a sector during disk operation, that defective sector will have its logical block address reassigned to a reassign spare pool. More specifically, the reassign spare pool, usually located at the end of the disk or tracks not used by user data, contains a number of unused sectors and are used to replace the defective sectors. The defect slipping method cannot be performed on grown defects found after the manufacturing process because the subsequent sectors already have data written in them. Changing the logical block address of these sectors would result in data lost or data miscompare, hence the defect reassignment method is used.
When a “grown defect” is detected, the logical block address corresponding to the “grown defect” location is reassigned to the reassign spare pool. The reassign spare pool normally resides at the end of the disk. When accessing the reassigned sector during read/write operation, extraneous seeks are required in order to retrieve the data which slows down the access time.
What is needed is a disc drive that operates with improved read/write performance when faced with “grown defects.” An improved method of defect management that eliminates extraneous seeks when attempting to retrieve data and permits all data sectors to be accessed in a continguous sequence in one revolution and an apparatus to implement such a method, is also needed.